Kimihiro Shibata

Dual-focus technique for high-power Nd:YAG laser welding of aluminum alloys

In order to apply aluminum alloys to structural components, they should be joined with sufficient strength and quality as high welding speed as possible. High-power laser welding is expected to achieve much higher productivity than conventional joining techniques. Welding of aluminum alloys was performed using 2-kW and 3-kW continuous wave Nd:YAG lasers. Two beams were delivered by optical cables 0.6 mm in diameter and focused on the surface of the specimens as dual spots. Overlap joints of 2-mm-thick sheets were made at various welding parameters, including beam distance, beam arrangement and welding speed. The quality of the bead, including its appearance and macrostructure, and the tensile strength of the joints were investigated. At a shorter beam distance of 0.36 mm, the weld bead surface was humped, making it unacceptable in terms of quality. Sound weld beads were obtained at beam distances of 0.6 mm and 1.0 mm. As the beam distance was increased, the weld depth became shallower. At a beam distance of 1.0 mm, the weld area was too small to provide sufficient strength.

Process stabilization by dual focus laser welding of aluminum alloys for car body

Aluminum alloys were welded using dual focus beams formed with two Nd:YAG lasers with the aim of obtaining a stable welding process. The relationship between the configuration of the spot beams and the quality of the weld beads was investigated using X-ray and high-speed camera observations. The number of pores was clearly related to the ratio of the keyhole depth to the keyhole opening. A larger keyhole opening and/or a shallower keyhole depth resulted in a smaller number of pores caused by instability of the weld pool. Based on the investigation, a car body component was welded with a dual focus beam system. The results show that aluminum car body panels can be welded stably at high speed with little distortion under optimum conditions.

Welding of aluminium car body parts with twin-spot high-power Nd:Yag laser

To reduce CO 2 gas emissions as a source of global warming, strenuous efforts are being made to improve the fuel efficiency of motor vehicles. Good progress is also being made in the development of technologies intended to reduce vehicle weight alongside improvement of power train efficiency. The car body accounts for some 25% of total vehicle weight, and substantial weight reduction can be achieved through car body manufacture from aluminium alloys in place of conventional steel. Application of aluminium alloys to car body panel components is therefore gathering pace. Through white bodies being extensively replaced by aluminium alloys, a weight reduction of more than 40% can be achieved compared with steel. Aluminium alloys, however, are a higher-cost material than steel and a low-cost joining method that simultaneously confers high reliability and good productivity is yet to be established. Applications of aluminium alloys to car body parts have accordingly been limited. Recent years have seen entry of the highpower Nd: YAG laser on the global market. This device has so far been used for three-dimensional welding of steel car bodies. Laser welding is also being increasingly used for welding of aluminium alloys in applications where spot welding and MIG welding were previously used. However, laser welding of aluminium alloys, chiefly for reasons of material properties, is apt to generate weld defects, such as hot cracking and blowholes, as well as other process instability-related defects, such as cavities and porosities. Some recent studies of laser welding of aluminium alloys have shown that parameters such as the focusing properties and laser power per unit keyhole depth, affect the occurrence of these defects and that application of a twin-spot beam is effective for process stabilisation and suppression of porosities. This article describes the study of welding of aluminium alloy car body parts by the twin-spot beam effective for welding process stabilisation. Its effectiveness is also investigated from the perspectives of weld quality and productivity. Al–Mg–Si alloy extrusions and rolled Al– Mg alloy sheets used for car body frames and panel components are welded with high-power Nd: YAG lasers and the joint performance is compared with those of MIG welding and resistance spot welding for the same parts. Joint strength and welding distortion are also evaluated.

Effect of alloying elements on weld properties in CO2 laser welding of aluminium alloys

To cope with requirements arising from environmental problems, particularly in the reduction of carbon dioxide from exhausts, the necessity to reduce the weight of vehicles is growing and has induced a large quantity of research and development in using aluminium alloys for vehicles. With this move, more and more investigations have been made on applying laser welding to the joints in the car body. Aluminium alloys have higher heat conductivity and greater linear expansion coefficient than steels and hence welding deformation tends to become a problem. For this reason, laser welding, whose heat source has a high energy density, has great potential as an alternative joining method to conventional MIG welding processes. However, it has not had many instances of applications, because it does not have high energy efficiency owing to the degree of laser beam reflection on aluminium alloys being higher than that of steels. To obtain the weld bead of keyhole type characteristic of the laser welding, the power density needed in the welding of aluminium alloys is said to be twice as high as that needed in the welding of steel materials. To improve mainly the strength, a variety of elements are often added to aluminium alloys. Structural alloys have elements such as Si, Mg and Zn added to them. These elements affect not only the dynamic properties of the alloys but also the thermodynamic characteristics and the thermal properties, and hence the difference in alloying elements is reported to affect laser weldability as well. The content of Mg and Zn, which have lower boiling points than aluminium, is known empirically to make a greater contribution to the formation of keyhole, but there has never been any quantitative evaluation of these effects. In this study, using a CO 2 laser, representative structural aluminium and its alloys were welded by varying the power density to find the power density (threshold) required to enable keyhole welding and its determining factors. By paying attention to the differences in thermodynamic properties and thermal conductivity which are induced by the alloying elements in various aluminium alloys, a further investigation was made of keyhole formation behaviour and its relationship with them.

Mechanical Properties of Aluminum Die Castings Welded by Nd:YAG Lasers

Abstract Reduction in vehicle weight is an essential technique for the improvement of automobile fuel efficiency. Consequently, there is an active programme of component weight reduction by replacement of current materials with aluminium alloys.

The effect of twin spot beam arrangement on energy coupling during welding. Study of twin spot Nd:YAG laser welding of aluminium alloys

Abstract Laser welding, regarded as one of the welding techniques for use with steel materials and employed in the fabrication of automobiles, has increasing applications in the manufacture of transmission systems and car bodies; however, there are not many examples of application to aluminium alloy components.1 The reasons for this are thought to be as follows: aluminium alloys have a higher laser reflectivity compared with that of steel materials; consequently an even higher power laser is required to input energy to the material for welding and also, due to the low viscosity of molten aluminium alloy, stable welding is difficult.2,3

Property of Laser Welded Bake-Hardening Steel in Tailored Blanks for Automobile

The behavior of bake-hardening of the laser weldment was investigated. The bake-hardening steel(BH steel) was welded with Nd:YAG laser followed by plastic deformation and subsequent heat-treatment. Then the influence of laser welding on the behavior of bake-hardening was investigated. The hardness of the laser weld metal significantly increased after welding. After the plastic deformation, both the base metal and weld metal became harder by work-hardening. The heat treatment resulted in more increment of hardness in both the base metal and weld metal by bake-hardening. The amount of bake-hardening reached a maximum value at the plastic strain of 5% or more. We modified a kinetic equation proposed for predicting the strength of a low-carbon bake-hardening steel and applied to the estimation of hardness of the base metal and weld metal. The calculated hardness values agree with the experimental data. The calculated activation energy for bake-hardenig was that for diffusion of carbon and nitrogen atoms in α-Fe. Thus the hardening is thought to be governed by diffusion of these solute atoms.

Real time x-ray observation of dual focus beam welding of aluminum alloys

In order to apply aluminum alloys to structural components, they should be joined with higher strength than that of the original materials. However, blowholes are apt to form in aluminum welding, because the process of melting and solidifying the material is unstable. Aluminum alloys were welded using 2-kW and 3-kW continuous wave Nd:YAG lasers with the aim of obtaining a stable welding process. Two beams were delivered by optical cables 0.6 mm in diameter and focused on the surface of the specimens as dual spots. At a shorter beam distance of 0.36 mm, the weld bead surface was humped, making it unacceptable in terms of quality. Sound weld beads were obtained at beam distances of 0.6 mm and 1.0 mm. X-ray observation was carried out in order to investigate the mechanism of process stabilization. A large keyhole opening that was observed at a large beam distance is thought to result in a stable welding process.In order to apply aluminum alloys to structural components, they should be joined with higher strength than that of the original materials. However, blowholes are apt to form in aluminum welding, because the process of melting and solidifying the material is unstable. Aluminum alloys were welded using 2-kW and 3-kW continuous wave Nd:YAG lasers with the aim of obtaining a stable welding process. Two beams were delivered by optical cables 0.6 mm in diameter and focused on the surface of the specimens as dual spots. At a shorter beam distance of 0.36 mm, the weld bead surface was humped, making it unacceptable in terms of quality. Sound weld beads were obtained at beam distances of 0.6 mm and 1.0 mm. X-ray observation was carried out in order to investigate the mechanism of process stabilization. A large keyhole opening that was observed at a large beam distance is thought to result in a stable welding process.